In species as diverse as chickens, mice, and humans, substantial numbers of T cells are constitutively associated with body surface epithelia, such as the gut, genitourinary tract, and the skin. Such intraepithelial lymphocytes (IELs) are commonly enriched in T cell receptor (TCR)gamma/delta+ cells, frequently with limited tissue associated antigen receptor diversity; thus, most IELs in mouse skin, also known as dendritic epidermal T cells (DETC), express strikingly homogeneous Vgamma5/Vdelta1 TCRs notable for their lack of junctional (CDR3 region) diversity. Combined use of different strains of TCRd-/- (knockout) mice and selective reconstitution of such mice via adoptive transfer has shown that Vgamma5+ DETC, but not other gamma/delta cells, are potent down-regulators of several physiologically relevant, cutaneous inflammatory responses, including a localized, genetically-dependent, TCRalpha/beta+ T cell-dependent environmentally-dependent, chronic dermatitis that shares several features of human atopic dermatitis. The long-term goal of this project is to utilize this powerful experimental model to define the mechanisms by which local T cells regulate the effects of systemic immune responses within local tissues. The specific aims of this project are: 1. To characterize in detail the cutaneous inflammation normally down-regulated by DETC) using: a) immunohistology, ex vivo flow cytometry, and microarray analysis; b) phenotypic comparisons of susceptible delta-/- mice with delta-/- mice also deficient in selected pro-inflammatory cells and/or molecules by virtue either of treatment with cytokine antagonists or blocking antibodies, or of a second "knockout" genetic mutation 2. To characterize the genes expressed by "resting" DETC and DETC "activated" in vitro by serial analysis of gene expression (SAGE), validate such analyses by quantitative RT-PCR of DETC in various in vivo and in vitro activation states, and compare such gene expression patterns with those both of gut-associated gamma/delta+ and alpha/beta+ IELs, and of systemic CD8+ alpha/beta+ "naive" and "memory" T cells. 3. To investigate selected candidate DETC anti-inflammatory cytokines/effector molecules by reconstituting delta-/- recipients with fetal thymic DETC precursors rendered deficient in candidate anti-inflammatory molecules. 4. To utilize genome-wide microsatellite mapping to identify the genetic interval(s) controlling susceptibility/resistance to the spontaneous dermatitis that develops in some, but not other d-/- mice, followed by additional studies (development of congenic lines, differential expression analyses of genes contained within this interval) directed at definitive identification of the gene(s) that regulate cutaneous inflammation.